Modulation
Overview In this level, you must master the skill of modulation and then make your way through the basics of radio to move onto the next level. Be warned traveler this is a very key concept in the lands of TC201. Antenna 9/16/10 Slide 13 *Conduct electromagnetic energy **Frequency **Power **Resonance **Tuned Antenna **Broadband Antenna **Directional vs. Omnidirectional **Size of antenna is inverse to the frequency of the wave ***AM radio tower ****361 feet ***Cellphone ****<3 inches Transduction *Conveyance of energy from one election (a donor) to another (a receptor), a the same time that the class of energy changes *What does that mean? **Adding energy can transfer between atoms, and be converted **i.e. electric to electromagnetic Summary of Wired Links 9/16/10 Slide 15-16 *Copper wire **Pass electrical waves **Bandwidth associated with gauge **Vulnerable *Wireless Links **Use the electromagnetic spectrum ***Digital Radio and Television Broadcasting Modulation 9/16/10 Slide 18 *Who is Fourier and what is his Theorem? **Combined and uncombined electromagnetic waves *Alter characteristics of carrier signal to enable it to carry information *What characteristics of a carrier can be modulated? **Amplitude **Frequency **Phase AM Process 9/16/10 Slide 20 *Input **Baseband/message-bearing signal *Modulation **The max. amplitude of the carrier is made to follow the instance *Modulation Index **100% **50% ***Vary the voltage **25% **150% ***If worried about static or noise or want to clean up *Spectrum of an AM wave **Fc = Carrier's frequency **Fm = Modulating signal's frequency **Located above and below the carrier frequency Frequency Modulation 9/16/10 Slide 36-37 *FM **The frequency of the carrier is made to vary in proportion to the changing amplitude of the modulating signal **The amplitude of modulated carrier remains constant *Sine Wave modulating a carrier **Freq. first increased, until input amp reaches peak **Then decreases to center, input at 0 **Then decreases to lowest level **… *FM Demodulation 9/16/10 Slide 43 **Limiter clips and filters to remove unwanted amplitude variations ***Outputs a constant amplitude fm signal **Discriminator ***Tuned circuit that outputs an amplitude proportional to frequency ***Actually converts fm to am **Then AM demodulation process Effect of Noise 9/16/10 Slide 44-45 *Noise **Any signal that does not convey useful information *Affected by additive noise **AM ***Yes **FM ***Relatively resistant to additive noise *Affected by impulse noise e.g. Lightning **AM ***Very susceptible **FM ***Much less susceptible *Signal-to-noise ration (S/N) **The bigger, the better *Signal-to-noise ration is 75 times better in FM than AM **Formula: 3 times the square of mod. Index *Max. Frequency of baseband signal **AM ***5 kHz **FM ***15 kHz ***Is much higher in fidelity than AM Guard Band 9/16/10 Slide 47 *A frequency band deliberately left vacant between two channels to provide a margin of safety against mutual interference **AM ***Practically no guard band **FM ***10 kHz on each side (20 kHz) **Broadcast TV ***100 kHz on each side (200 kHz) *AM Radio **BW of AM station in US ***Between 525 and 1705 kHz ***10 kHz channel ***No real guard band ***117 available channels ***Separated geographically **Uses a "groundwave" **Reflects off the ionosphere *FM Bandwidth **BW of FM station in US ***Max. frequency deviation = 75 kHz (FCC regulated) ***Baseband signal = 15 kHz ***BW = (2 x 75) + (2 x 15) = 180 kHz ***Adding a 10 kHz guard band at each end, the total spectrum assigned to a FM station is 200 kHz ***Does not use a groundwave (line of sight) **No worries on ionsphere *AM vs FM **AM ***10 kHz bandwidth from 540-1600 kHz for possible bands Radio Basics 9/16/10 Slide 48 AM Radio *Tuner *Detector *Amplifier *Speaker Basic Models *Shannon-Weaver Model *Mathematical Model (1949) *Process **Information Source **Message **Transmitter (Encoder) **Channel **Received Signal **Receiver (Decoder) **Destination ***Noise Source **Concepts ***Entropy ***Redundancy ***Noise ***Channel Capacity [[Digital Basics|'CONTINUE...' ]] [[TC201 Giga Wiki|'MENU' ]] References